The present invention relates, in general, to metallurgical fields, and, more particularly, to production of shot, powder, and particle generation.
The process of shot peening is commonly used to create surface compressive stresses in stainless steel material (particularly in or near welded areas) for the prevention of stress corrosion cracking, which otherwise occurs when surfaces are exposed to heated water containing chlorides and subject to surface tensile stresses. The process is also used for improvement of fatigue resistance. Present production techniques for stainless steel shot involve cutting wire with or without subsequent processing to round the edges of the cuts. This process is neither cost-effective nor capable of producing truly spherical material.
Stainless steel shot is produced primarily by cutting a drawn wire and, in some cases, in the prior art, conditioning this wire to round the edges of the cut. This prior art process is costly and does not yield the spherical shape most desirable for purpose of shot peening. Metallic shot from certain metals can be produced in a shot tower where the molten metal is broken up by screening and allowed to cool by dropping the distance provided in the shot tower. Shot has also been produced in prior art methods by directing a stream of molten metal onto a rotating spinning disc which causes break-up of the metal by centrifugal force.
Other approaches are disclosed in U.S. Pat. Nos.: 2,308,584, 2,341,704; 2,523,454; 2,567,121; 2,636,219; 2,428,718; 3,891,730; and 3,951,577. All of the approaches disclosed in these patents involve the intersection of a stream of fluid and a stream of molten metal to break up that stream of molten metal and produce shot.
Powders used in powder metallurgy, compacting or sintering, are frequently broken up by high pressure water streams or may be produced by rotary spinning devices as used for some types of shot.
The above-discussed processes do not provide the degree of adjustability and versatility required for modern techniques, nor do such processes readily provide ability to introduce modifying elements into the particles.